GIANT KANGAROOS wiped out by humans, not climate change

In a land before time – or at least Australia about 40,000 years ago – five meter kangaroos bounded across the landscape. Some were fleeing colossal marsupial lions. Others were trying to stay out of the way of Emus twice the size of today's specimens or Diprotodon Optatum, a rhinoceros-like beastie that was the largest marsupial of all time.

Then in not very many years all of these animals died, leaving scientists rather confounded about just why.

One theory has been that Australian Aboriginals arrived around 40,000 years ago. The marsupial megafuana, previously unchallenged at the top of the food chain and therefore lacking aggressive predators, quickly succumbed to the hunter-gatherers' weapons.

An alternative theory suggested that climate change did them in, by altering the environment in ways that were no longer conducive to massive creatures and their considerable calorific requirements.

The latter theory has just taken a hit, thanks to a new paper in Science by Dr Susan Rule from Australian National University and Professor Christopher Johnson from the University of Tasmania. The pair analysed sediments from a fossilised swamp in Queensland, focusing on the presence of spores from a fungus called Sporormiella that is known to have been present in the dung of ancient herbivores. Lots of Sporormiella, the pair argue, would mean lots of megafauna.

The pair found precious little Sporormiella in samples about 40,000 years old. They also looked at other records of pollen counts and prevalence of charcoal.

The results suggested that Sporormiella counts dropped ahead of a change in plant types and an increase in the incidence of fires.

The pair hypothesise that this shows the megafauana were hunted to extinction, removing Australia's most voracious grazers and therefore allowing more plants to grow. That accounts for the pollen changes and the increased fire, as fewer grazing animals means more fuel for fires.

Other researchers have criticised this logic, as apparently Sporormiella prevalence is accepted as an indicator for the presence of herbivores in New Zealand, Madagascar and the USA. Science awaits a strong link between Australian herbivores and Sporormiella. ®